Affiliations: San Francisco, CA ,
Phoenix, AZ ,
Dr. Boushey is Professor of Medicine, University of California, San Francisco. Dr. Enright is Professor of Epidemiology and Biostatistics, University of Arizona.
Correspondence to: Homer Boushey, MD, Box 0130; 1292-M, University of California San Francisco, 505 Parnassus Ave, San Francisco, CA 94143-0130; e-mail: email@example.com
A theme of the newly released Guidelines for the Diagnosis and Management of Asthma of the National Institutes of Health (http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm) is that asthma severity and asthma control must be considered in two domains. The first, “current impairment,” is a function of the frequency and severity of symptoms, nocturnal awakenings, and interference with ability to perform tasks. The second, “future risk,” is a function of the risk of exacerbations, progressive loss of pulmonary function, or progression to a more severe form of asthma.
Assessment of asthma severity or control in the first domain is usually straightforward, and is done by direct inquiry, perhaps facilitated by one of several standardized questionnaires (eg, The Asthma Control Test,1Asthma Control Questionnaire,2or Adult Asthma Therapy Assessment Questionnaire3–). Assessment of “future risk” is problematic because the evidence base relating measurements made at baseline to the rate of exacerbations or loss of pulmonary function over an extended follow-up period is slender. The evidence that is available suggests that a history of severe or frequent exacerbations in the past identifies a patient as at risk for their recurrence in the future,4–5 but it certainly suboptimal to have to wait until patients have had exacerbations before being able to tell them that they are at risk for them.
It is in this context that the findings of Osborne et al6 (see page 1151) of the “profile of asthma risk” are particularly important. Their large, prospective study of the predictors of asthma exacerbations in adults provides validated, simple instruments that accurately classify patients as at low, medium, or high risk for exacerbations. One instrument (instrument A) uses nine questions; another (instrument B) uses only four questions and prebronchodilator FEV1, and the third (instrument C) uses four questions, prebronchodilator FEV1, and the results of allergen skin testing to dog and cat antigen.
Of all the individual predictors analyzed, prebronchodilator FEV1 expressed as percentage of predicted was by far the most powerful. An FEV1 of 60 to 80% of predicted was associated with a 2.43-fold increase in the relative risk for exacerbation. An FEV1 < 60% of predicted was associated with an increase in the relative risk to 4.61-fold. Adding information from spirometry to the information from other sources increased predictive power even more. Instrument B (with spirometry) was much more powerful than instrument A (without spirometry). Compared to the low-risk group, patients placed in the medium-risk group by instrument B were 3 times more likely to require hospital-based urgent care for an asthma exacerbation during the subsequent 30 months; those placed in the high-risk group were 11 times more likely. For example, a man who missed some work due to asthma (1 point), saw a doctor because of acute shortness of breath during the previous year (1 point), had an emergency department visit for breathing problems 5 years ago (2 points), and currently has an FEV1 of 55% of predicted (4 points) is categorized as high risk (8 points total). He has about a 50:50 chance of needing an urgent care visit for asthma during the next 3 years. Knowledge of this high risk is important because the cost of asthma exacerbations exceeds 3 billion dollars per year in the United States, and most can be prevented. Use of the simple instruments developed by Osborne et al6 allows identifying patients at high risk for these exacerbations and initiating effective treatment for them.
The study has some limitations. It did not provide data on the rate of loss of pulmonary function, and it did not analyze the effects of treatment on the predictive power of the various instruments. Does, for example, a low FEV1 have the same predictive significance in a patient receiving an inhaled corticosteroid as in one receiving only “rescue” β-agonists? Would the bronchodilator-induced change in FEV1 be even more powerful than baseline FEV1 in predicting risk? And by limiting the study to patients aged 18 to 55 years, the study may have underestimated the actual power of spirometry in predicting risk, for poor perception of airway obstruction is more common in older adults.7 Even so, Osborne et al6 provide simple, easily used tools that can be put to immediate use. They also set a standard by which other predictive tests, such as measurement of exhaled nitric oxide or enumeration of eosinophils in induced sputum samples, should be assessed.
More work needs to be done, but this study provides sound evidence for the National Asthma Education and Prevention Program guidelines recommendation for periodic spirometry testing (http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm). While the latest update of the guidelines allows the use of either peak expiratory flow or FEV1, the results are not interchangeable.8–10 Offsetting the low cost of mechanical peak flow meters, the FEV1 is more accurate, more repeatable, less effort dependent, and predicted values for FEV1 are firmly established.11
We urge government and industry investigators to design randomized clinical trials using instrument B in other primary care settings with a wider range of ages, ethnic groups, and environmental conditions. The participating physicians should use the results of the instrument to encourage appropriate lifestyle changes (such as smoking cessation, allergen avoidance, and reduction of workplace exposures), to initiate appropriate therapy (especially inhaled corticosteroids) and/or to encourage better adherence to them. Should these studies confirm that these interventions, based on the tools developed by Osborne at al, lead to a significant reduction in exacerbation rates, the way will be clear for broad implementation of a simple approach to reducing the cost and morbidity of a common and costly disease.
Dr. Boushey has no pertinent conflicts of interest on this topic.
Dr. Enright has received five free lunches or dinners from ndd Medical Instruments, a manufacturer of spirometers, during the previous 3 years, but has no other pertinent conflicts of interest on this topic.
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